1. Technical Field
The object of the present invention is a process for collectively making integrated magnetic heads with a rounded bearing surface.
It finds an application in the making of helical magnetic tape recording heads, particularly for consumer or professional video recording (living room video recorders, camcorders) or again for computer data tape or disk recorders. It also finds application in other recording heads for tapes, disks, cards, etc.
The high frequencies permitted by the small size of integrated thin film heads allow digital recording (for example in accordance with the DVC standard for video, or DDS for IT). Data tape recorders are computer file stores having the largest storage capacities and the lowest costs. Computer applications are data storage, hard disk back-up systems for a system or a large software or database broadcasting network. In the field of video recording, it is conceivable for video recorder applications to be broadened to those of a video server centralising several films.
2. Field of the Invention
The appended FIGS. 1 to 3 show the structure of a component for a thin film integrated magnetic head according to the document FR-A-2 747 226. As shown the head includes (FIG. 1), two pole pieces 101, 102 separated by an air-gap 14, two magnetic branches 161, 162 partially covering the pole pieces, and a magnetic flux close piece 18. These pieces taken together constitute a magnetic circuit. Around the branches 161, 162 are found conductor windings 201, 202 providing read and/or write of the written and/or read data on a recording medium not shown.
FIG. 2 shows the complete head with two conductor bands 221, 222 allowing access to the conductor windings 201, 202 and two electrical connection jacks 241, 242.
The head shown in FIGS. 1 and 2 may be made in a collective way using technologies borrowed from micro-electronics. To obtain an individual magnetic head from a wafer including a plurality of components, the components may be separated from each other, by ordering them for example in a matrix structure, then by cutting them along straight paths. By machining the front part of the components, each head, in the vicinity of the pole pieces 101, 102, is given a bearing surface of rounded shape necessary for the proper operation of the head. In FIG. 2, the rounded profile is shown diagrammatically by the line 26. This operation is carried out mechanically on each head.
FIG. 3 shows, in a diagrammatic way, a head seen in cross-section along one of the conductor bands and one of the branches of the magnetic circuit. A substrate 30, for example of silicon, may be seen with one of the pole pieces 101, or 102, a magnetic branch 161, or 162, a magnetic close piece 18, a conductor band 221, or 222 and the electrical connection jacks 241, 242. The whole is covered by a superstrate 40, for example of silicon. Towards the front of the head, the surface 26, called a bearing surface, has an appropriate rounded shape. Towards the back, the superstrate 40 is disengaged so as to reveal the electrical connection jacks 241, 242.
Although the processes for making such magnetic heads are largely collective, the fact is nonetheless that the final stage of manufacturing the bearing surface 26 is individual and adds considerably to the final cost of each head. However, through the document U.S. Pat. No. 4,418,472, a collective process is known which uses ion machining but which is only applied to straight surfaces. This process is not appropriate for rounded surfaces with, additionally, the low dimensions of current digital recording heads. The radius of curvature of the head near the air-gap is an essential parameter in obtaining good head/band contact, and therefore good quality of recording and control of wear and tear: too large or too small a radius of curvature may lead either to bad contact quality (and therefore excessive attenuation of the head signal), or to accelerated wearing of the head. Furthermore, grinding makes it difficult to machine very precise radii of curvature or different radii of curvature on the bearing surface.
Indeed the purpose of the present invention is to overcome these drawbacks.
To this end, the invention proposes a process for collectively making integrated magnetic heads wherein:
on a wafer are made a plurality of components each including means able to constitute at least one magnetic head and particularly pole pieces separated by an air-gap,
the wafer is machined collectively so as to give to all the components, in the vicinity of the pole pieces, a surface having an appropriate shape;
the components are then separated, the surface thus engraved in the vicinity of the pole pieces constituting the bearing surface of each of the heads,
this process being characterised in that said appropriate shape is a rounded shape with at least one radius of curvature, wherein the wafer is machined collectively either by masked photolithography, or by cutting by means of a laser beam.
In a first alternative:
on the wafer is deposited at least one mask including as many patterns as components on the wafer, each pattern having, opposite the pole pieces of each component, an edge of rounded shape;
the wafer is engraved collectively by photolithography through this mask or these mask to give to all the components, in the vicinity of the pole pieces, a surface having said rounded shape.
In a second alternative, a laser beam able to cut the wafer at least partially is directed onto the wafer and the laser beam is moved along a rounded path. Preferably, the laser beam is guided by a jet of liquid at high pressure, for example water.